Remote position location systems are used in a wide range of applications. In some cases, GPS may be used to determine the position of a GPS-receiving device. In others, a terrestrial set of RF transceivers may communicate with the target object using RF communications and triangulation may be used to pinpoint the object's location. Various triangulation techniques exist and may rely upon signal strength, time-of-arrival, angle-of-arrival, or other such techniques. However, any of these techniques rely upon the target object being in an RF-friendly environment. GPS only functions correctly if the target object is able to receive RF GPS signals from satellites. RF triangulation only functions correctly if the target object is able to reliably receive the terrestrial RF signals without excessive attenuation or multi-path problems. In many environments, such as underwater, underground, or in-building, conventional position location systems are inoperable.
Similar reference numerals may have been used in different figures to denote similar components.